The invention generally relates to a fluid-flow machine. More preferably, it relates to a fluid flow machine including a rotor which extends along a rotation axis. The rotor preferably includes a rotor-shaft slot and a moving blade having a blade root which is inserted into the rotor-shaft slot, and a gap being formed between the blade root and the slot root surface. The invention also generally relates to a sealing element for a rotor of a fluidflow machine.
Rotatable moving blades of fluid-flow machines, for example of gas or steam turbines or compressors, are fastened in different configurations over the full circumference to the circumferential surface of a rotor shaft, which, for example, has a rotatable moving disk. A moving blade in this case normally has a blade body, a blade platform and a blade root having a fastening structure which is accommodated by a rotor-shaft slot configured in a corresponding complementary manner for fixing the moving blade. In this case, the rotorshaft slot may be produced as a circumferential slot or axial slot on the circumferential surface of the rotor shaft. The rotor-shaft slot has a slot root surface.
Due to the design, after the blade root of a moving blade has been inserted into the rotor-shaft slot, a gap is formed by the rotor components adjacent to one another in each case. During operation of the rotor, the gap gives rise to leakage flows of cooling medium or of an action fluid driving the rotor through the gap. Such a gap is formed between the blade root and the slot root surface. A gap of this type may also occur between two adjacent blade platforms of moving blades which are adjacent in the circumferential direction and between the circumferential surface of the rotor shaft and a blade platform radially adjoining the circumferential surface.
In order to limit the possible leakage flows through the gap, such as, for instance, the escape of cooling medium, e.g. cooling air, into the flow passage of a gas turbine, intensive searches are being made for effective sealing concepts. These sealing concepts must be resistant to the temperatures which occur and to the mechanical loading as a result of the considerable centrifugal forces on the rotating system.
DE 198 10 567 A1 discloses a sealing plate for a moving blade of a gas turbine. If cooling air which is fed to the moving blade escapes into the flow passage, this leads, inter alia, to a reduction in the efficiency of the gas turbine. The sealing plate, which is inserted into a gap between the blade platforms of two adjacent moving blades, is intended to prevent the leakage flows resulting from the escape of cooling air. An additional sealing effect is achieved by sealing pins which are likewise fitted between the blade platforms of two adjacent moving blades. A multiplicity of sealing pins are required in order to achieve the desired sealing effect to prevent the escape of cooling air from the adjacent blade platforms.
A sealing concept for a rotor of a gas turbine having a moving disk and a moving blade cooled in the interior is described in U.S. Pat. No. 4,021,138. The moving disk has a front face, a rear face located opposite the front face along the rotation axis, and an axial moving-disk slot which extends from the front face into the rear face. The moving blade has a blade root which is accommodated by the axial moving-disk slot. In the moving disk, a cooling-medium chamber is adjacent to the blade root in a radially inward direction and passes completely through the moving disk in the axial direction from the front face up to the rear face.
Provided in the moving blade are cooling-medium passages which extend from the blade root up to the blade body in the radial direction and are in fluidic connection with the cooling-medium chamber, so that, for the internal cooling of the moving blade, a cooling medium passes from the cooling-medium chamber into the cooling-medium passages. For this purpose, a cooling medium is admitted to the cooling-medium chamber via a cooling-medium feed arranged axially upstream of the front face. In order to seal the cooling-medium chamber against an escape of cooling medium, a first sealing plate is arranged on the front face and a second sealing plate is arranged on the rear face of the moving disk. For improved sealing, that side of the first sealing plate which faces the front face has a passage which extends in the circumferential direction of the moving disk and opens toward the front face.
The passage is defined in the radial direction by an outer marginal region arranged radially outward and by an inner marginal region located opposite the outer marginal region and arranged radially inward, the outer and inner marginal regions adjoining the front face. The outer marginal region is configured in such a way that, as a result, that part of the passage which adjoins the front face is inclined in a direction relative to the normal of the front face, this direction having a radially outward component. A sealing rod which extends in the circumferential direction is inserted into the passage in such a way as to be movable.
During operation of the rotor, the sealing rod, under the effect of centrifugal force, moves radially outward in the passage along the outer marginal region and in a direction toward the front face, where it finally assumes its sealing position. In the sealing position, the sealing rod is in contact with the front face and seals a gap which is formed between the front face and that side of the sealing plate which faces the front face. This is intended to largely prevent cooling medium from escaping through the gap from the cooling-medium chamber or the cooling-medium feed. This solution is very costly due to the use of the relatively extended sealing plates and the additional sealing rods. Furthermore, maintenance and repair work on the moving blade is only possible after complete removal of these sealing components from the rotor.
EP 0 799 974 A2 discloses a sealing element for a moving blade of a turbomachine. In this case, the turbomachine has a rotor with a rotor disk arranged radially inward, a multiplicity of moving blades being fastened radially outward to the rotor disk in the circumferential direction of the rotor disk with a respective gap being formed. To cool the rotor, cooling passages are provided which extend in the radial direction through the rotor disk and the moving blades.
In order to limit an escape of cooling medium (leakage) from the gap in the region of the blade fastening, a sealing element is arranged between the blade root and the rotor disk. The sealing element, under the effect of centrifugal force, performs a tilting movement and thereby reaches its sealing position. In order to secure the sealing element in the direction of the rotation axis in such a way as to prevent it from falling out of the gap, the sealing element has two securing teeth which enclose a projection, formed radially inward, in the blade root, the sealing element, in particular one of the securing teeth, projecting at least partly from the gap at the front face of the rotor disk.
An object of the invention is to specify a fluid-flow machine including a rotor which has a rotor-shaft slot and a slot root surface and a moving blade with a blade root, the blade root being inserted into the rotor-shaft slot, with a sealing element. Preferably, the sealing element is intended to make it possible to efficiently limit axial leakage flows and is to be as resistant as possible to the mechanical and thermal loads which occur. A further object of the invention is to specify a sealing element, in particular for a rotor of a fluid-flow machine.
According to the invention, the first-mentioned object is achieved, for example, by a fluid-flow machine including a rotor which extends along a rotation axis and has a rotor-shaft slot having a slot root surface and a moving blade having a blade root, the blade root being inserted into the rotor-shaft slot, and a gap being formed between the blade root and the slot root surface. A sealing element is preferably provided for sealing the gap. The sealing element is further preferably at least partly accommodated by the blade root. In addition, the sealing element is preferably movable relative to the blade root, and is in contact with the slot root surface under the effect of centrifugal force and thereby sealing the gap.
During operation of a fluid-flow machine, for example of a gas or steam turbine or of a compressor, the rotor is preferably exposed to an action fluid, e.g. a hot gas, steam or heated air, flowing along this rotor. In the process, an action fluid, as a result of expansion, can preferably perform work on the moving blades and set the latter in rotation about the rotation axis. The rotor having the moving blade can be subjected to both very high thermal and mechanical loading, in particular by the centrifugal forces occurring as a result of the rotation. A cooling medium, e.g. cooling air, is preferably used to cool the rotor and in particular the moving blade, this cooling medium normally being fed to the rotor through suitable cooling-medium feeds. In this case, leakage flows of both cooling medium and flowing action fluidxe2x80x94xe2x80x9cgap lossesxe2x80x9dxe2x80x94may occur in the gap formed by the blade root and the slot root surface. These leakage flows have a very adverse effect on the cooling efficiency and on the mechanical installation strength (smooth running and creep strength) of the moving blade in the rotor-shaft slot.
A new way of effectively sealing the gap against possible leakage flows is preferably provided. This may be achieved, on the one hand, by the sealing element being at least partly accommodated by the blade root and being movable relative to the latter. On the other hand, the centrifugal force occurring during operation of the fluid-flow machine, i.e. during rotation of the rotor, may be deliberately utilized for sealing purposes. In addition to the fastening of the moving blade, the blade root therefore can serve at the same time to accommodate the sealing element.
Furthermore, the sealing element is preferably guided in the blade root by the configuration specified. The gap extends in the radial direction and axial direction and also in the circumferential direction of the rotor, the axial extent of the gap normally being predominant, and the extent of the gap in the circumferential direction being greater than the radial dimension. The precise geometry of the gap is determined by the specific configuration of the rotor-shaft slot and of the slot root surface and also of the blade root. In this case, the sealing element may be adapted individually to the respective geometry of the rotor and to the requirements with regard to the leakage flows to be limited.
According to the invention, the sealing element preferably seals the gap under the effect of centrifugal force. During operation of the fluid-flow machine, the sealing element, as a result of the rotation, is then brought into its sealing position by the centrifugal force directed radially outward and develops its sealing effect. In the process, the sealing element is firmly pressed against the slot root surface and seals the gap.
A considerable advantage compared with conventional sealing concepts can be obtained due to the specific sealing of the gap, for example. In this way, it is possible to realize a very compact type of construction. Extended sealing elements, which are very costly, are therefore unnecessary. The sealing element is arranged locally where it is required for efficiently limiting leakage flows.
During operation of the rotor, the sealing element preferably reaches its sealing position in the process and develops its sealing effect. In this case, the sealing element comes into contact with the slot root surface and is pressed firmly against the slot root surface. Furthermore, owing to the fact that the sealing element is at least partly accommodated by the blade root, the gap is sealed.
In this way, for example, the ingress of an action fluid, e.g. of the hot gas in a gas turbine, into the gap is effectively prevented. This protects the material of the rotor, in particular the material of the blade root, from the high temperatures and the possible oxidizing and corrosive influences of the action fluid. Owing to the fact that leakage flows of action fluid and/or cooling medium in the gap are prevented by the sealing element, temperature gradients in the region of the blade fastening are avoided. Possible thermal stresses which result from an impaired thermal expansion of adjacent rotor components during temperature differences are thereby reduced. The blade root of a moving blade and the rotor-shaft slot which accommodates and fixes the moving blade may therefore be produced with a markedly smaller tolerance. A smaller tolerance dimension has an advantageous effect on the mechanical installation strength of the moving blade and on the smooth running of the rotor.
In particular, fits which are preferably provided for fastening the blade root in the rotor-shaft slot may be provided with a smaller clearance. This also correspondingly reduces the possible leakage flows through the fit. Since the sealing element is at least partly accommodated by the blade root, it is securely held and secured against falling out of the rotor, on the one hand, and is protected from being directly acted upon by the action fluid, on the other hand. In this case, the sealing element is not necessarily firmly coupled to a moving blade, in particular to the moving-blade root. This facilitates assembly and repair work on a moving blade, such as, for example, the exchange of a moving blade, without a relatively large effort. The sealing element remains largely unaffected by this and can therefore also be used repeatedly.
The rotor preferably has a moving disk which includes the rotor-shaft slot with the slot root surface, the rotor-shaft slot extending along a transverse axis which is inclined relative to a plane perpendicular to the rotation axis. The fastening of the rotatable moving blade in the rotor-shaft slot is thus produced in such a way that, during operation of the rotor, it can absorb, with a high degree of certainty, the blade stresses caused by flow and centrifugal forces and by blade vibrations and can transmit the forces which occur to the moving disk and finally to the entire rotor. The fastening of the moving blade may be effected, for example, by axial slots, a moving blade being secured in position in a moving-disk slot provided specially for this and extending essentially in the axial direction. For low stresses, e.g. in the case of moving blades in axial-flow compressors, simple fastenings of the moving blade, for example with a dovetail or Laval root, are possible. For steam-turbine end stages having long moving blades and correspondingly large blade centrifugal forces, in addition to the xe2x80x9cpush-in rootxe2x80x9d, the axial fir-tree root is also suitable. The axial fir-tree fastening is preferably also used in thermally highly loaded moving blades in gas turbines. In this case, the rotor-shaft slot may extend entirely across the entire moving disk along the transverse axis. The gap between the slot root surface and the blade root is then open radially and accordingly extends along the transverse axis.
The sealing element is preferably arranged in a recess, in particular in a slot, in the blade root. The sealing element is secured against falling out and/or against being thrown out by the effect of centrifugal force during steady-state operation or during transient loading of the rotor by the sealing element being arranged in a suitable recess in the blade root. In addition, a reaction surface is produced in the blade root by the recess, this reaction surface expediently being designed as a sectional surface of the recess. In the case of a slot, this reaction surface is produced, for example, on the slot root. The reaction surface is then arranged radially outward in the blade root and is located opposite the slot root surface of the rotor-shaft slot in the radial direction.
To achieve as good a sealing effect as possible during the engagement of the sealing element in the recess, the reaction surface may be produced with correspondingly small and well-defined surface roughness. After the actual production of the recess, in particular of the slot, for example by stock removal from the blade root by means of a milling or turning operation, a reaction surface having the desired roughness can be produced on the slot root by polishing.
The blade root preferably has a first blade-root margin and a second blade-root margin, located opposite the first blade-root margin along the rotation axis, and a blade-root center region which is arranged axially between the first blade-root margin and the second blade-root margin, a sealing element being arranged in the region of the first blade-root margin and/or of the second blade-root margin and/or of the blade-root center region. In this case, for example, relative to the direction of flow of a flowing action fluid, for example of a hot gas of a gas turbine, the first blade-root margin 47 is arranged upstream and the second blade-root margin 51 is arranged downstream. Depending on the design conditions and requirements with regard to the sealing effect to be achieved in the gap, this geometrical division permits a configuration and arrangement of the sealing element or of a plurality of sealing elements in various sections of the blade root.
The arrangement of a sealing element in the region of the first blade-root margin arranged upstream primarily limits the ingress of flowing, possibly very hot, action fluid into the gap and therefore prevents damage to the rotor. The arrangement of the sealing element in the region of the second blade-root margin arranged downstream mainly serves to limit the escape of cooling medium, e.g. cooling air under a certain pressure in the gap, upstream in the axial direction along the slot root surface into the flow passage. Since the action fluid expands in the flow direction, the pressure of the action fluid is continuously reduced in the flow direction. A cooling medium under a certain pressure in the gap will therefore escape from the gap in the direction of the lower ambient pressure, that is to say at the second blade-root margin arranged downstream. For this reason, it is advantageous to provide a sealing element in the region of the second blade-root margin. The blade-root center region forms a further section of the blade root. Together with the first and the second blade-root margin, there are therefore different possibilities available for arranging a sealing element in various sections of the blade root. In this case, in moving blades which have an internal cooling system, a cooling medium, e.g. cooling air, being fed by a suitable cooling-medium feed which is arranged in the blade-root center region, the sealing element will preferably be arranged in the region of the first or the second blade-root margin. In moving blades without such an internal cooling system, the sealing element may be arranged just as advantageously in the region of the blade-root center region.
A plurality of sealing elements are preferably provided. The number and arrangement of the sealing elements is determined depending on the design conditions and requirements with regard to the sealing effect to be achieved, it also being possible for combinations of several sealing elements to be used. The sealing concept offers very high flexibility with regard to the adaptation to an actual task definition. For example, the combination of a sealing element in the region of the first blade-root margin and a further sealing element in the region of the second blade-root margin seals the gap from two sides and therefore provides a high degree of safety both against an ingress of action fluid into the gap and against an escape of cooling medium from the gap into the flow passage of the fluid-flow machine. An escape of cooling medium into the flow passage would lead, inter alia, to a reduction in the efficiency of the fluid-flow machine. A multiple arrangement of sealing elements is also very advantageous in this respect.
The sealing element preferably extends in a plane perpendicular to the rotation axis. The gap has a radial extent and an axial extent and also an extent in the circumferential direction of the rotor. A sealing element extending in a plane perpendicular to the rotation axis is therefore especially suitable for obstructing possible axial leakage flows in a highly efficient manner. Thus, for example, an axial leakage flow directed upstream, e.g. a hot gas from the flow passage of a gas turbine, this leakage flow spreading along the slot root surface, is effectively obstructed by the sealing element. In the process, the leakage flow is retarded in the gap by the obstacle in the form of the sealing element and finally comes to a stop on that side of the sealing element facing the leakage flow (single choke). That side of the sealing element which faces away from the leakage flow and the adjoining part of the gap in the axial direction are already protected by the single sealing element from being acted upon by the leakage medium, e.g. a hot action fluid or a cooling medium. A marked improvement in this single solution with an individual sealing element which extends in a plane perpendicular to the rotation axis is obtained by the combination of the sealing element with one or more further sealing elements which likewise extend in a plane perpendicular to the rotation axis and which are arranged at an axial distance from the sealing element. Possible leakage flows in the gap are considerably reduced by this multiple arrangement of sealing elements.
The sealing element is preferably movable in the radial direction. This achieves the effect that the sealing element moves away from the rotation axis of the rotor in the radial direction under the effect of centrifugal force. This effect is deliberately utilized in order to achieve. a markedly improved sealing effect in the gap. In the process, the sealing element, under the effect of centrifugal force, comes into contact with a reaction surface which is arranged radially outward and is configured, for example, as a sectional surface of a recess, in particular of a slot. The sealing element is pressed firmly against the reaction surface. Appropriately advantageous utilization of the centrifugal force and of the reaction forces and their force components at the reaction surface achieves the effect that the sealing element at the same time comes into contact with the slot root surface and is pressed firmaly against the slot root surface. Sufficient radial mobility of the sealing element is ensured by suitable dimensioning of the recess, in particular of the slot, in the blade root and of the sealing element.
Furthermore, it is advantageous that, as a result, the sealing element, for any possible maintenance purposes or in the event of a failure of the moving blade, can be removed from the recess without any problems and if need be exchanged without additional tools and without the risk of caking of the sealing element on account of an oxidizing or corrosive attack at high operating temperatures. In addition, a certain tolerance of the sealing element, which engages in the recess, in particular in the slot, in the blade root, is very useful, since thermal expansions are thereby permitted and consequently thermally induced stresses between the sealing element and the adjoining slot root surface and the blade root are avoided.
The sealing element preferably has a first sealing element section and a second sealing element section which are movable relative to one another. In this case, the sealing element sections may be configured in such a way that, in a special manner, they perform a partial sealing function for different regions in the gap which are to be sealed, in particular for different regions of the slot root surface. The sealing element sections, by their paired arrangement, then complement one another to form one sealing element, the sealing effect of the paired system consisting of sealing element sections being greater than that of a single sealing element section.
A configuration of the sealing element sections which is especially adapted to the regions in the gap which are to be sealed in each case makes it possible for the sealing effect of the paired arrangement to be greater than would be realizable with a one-piece sealing element. An especially flexible and efficient system of sealing element sections is therefore provided by the relative mobility of the sealing element sections. In this case, both relative translations and rotations of the sealing element sections relative to one another are envisaged. Provided the sealing element sections extend, for example, in a plane perpendicular to the rotation axis, the relative movements are restricted essentially in this plane. The relative mobility of the sealing element sections permits a highly adapted system, which is configured according to the thermal and/or mechanical loading of the rotor and according to the specific geometry of the gap to be sealed. In this case, the adapted system of sealing element sections is configured and mounted in such a way that it adjusts itself, as it were, under the effect of the external forces, such as, for example, the centrifugal force and the normal or bearing forces (reaction forces), and develops its sealing effect in the process. Furthermore, the movable pair of sealing element sections advantageously compensates for possible thermally or mechanically induced stresses in a markedly better manner than in the case of conventional sealing concepts.
A first rotary region having a first rotary axis is advantageously assigned to the first sealing element section, and a second rotary region having a second rotary axis is advantageously assigned to the second sealing element section.
Each of the sealing element sections is therefore preferably designed in such a way that it mounted so as to be rotatable about a respective rotary axis. If the sealing elements extend in a plane perpendicular to the rotation axis, the rotation of the sealing element sections is restricted in this plane. Improved sealing of the gap is made possible as a result, since each sealing element section is brought into a favorable sealing position by the rotation. In this way, an improved sealing effect is independently achieved for each sealing element section. In this case, the rotary axis of a sealing element section may also be formed as a supporting point (supporting axis) of the rotary region with a suitable supporting surface, e.g. with a reaction surface which adjoins the rotary region. The reaction surface is advantageously produced as a sectional surface of a recess, in particular of a slot, in the blade root. In this case, the first rotary axis and the second rotary axis may be different from one another or identical. In the latter case, the first sealing element section and the second sealing element section have a common rotary axis.
The mass center of the first sealing element section is preferably arranged relative to the first rotary axis and the mass center of the second sealing element section is preferably arranged relative to the second rotary axis in such a way that the torques resulting under the effect of centrifugal force are opposed. Due to the resulting opposed torques, the sealing element sections are rotated relative to one another in an opposite direction about the respective rotary axis. The centrifugal force acts radially outward in the same way for both sealing element sections and acts at the respective mass center. Here, the perpendicular connecting vector from the mass center of one of the sealing element sections to the associated rotary axis, together with the centrifugal-force vector, forms, for example, a right-handed system. In this case, the perpendicular connecting vector from the mass center of the other sealing element section to the rotary axis assigned to the other sealing element section, together with the centrifugal-force vector, forms a left-handed system, so that the resulting torques are opposed. This is ensured by appropriate design of the sealing element sections with regard to the mass distribution, in particular the position of the respective mass center and the mounting of the sealing element sections with regard to the rotary axis.
The first sealing element section and the second sealing element section preferably have similar geometry. The sealing element sections may therefore be transformed into one another by rotations or mirror inversions or symmetry operations combined therefrom. This is an especially favorable solution from the production point of view, especially if the first sealing element section and the second sealing element section are of identical design. It is then only necessary to produce one form of the sealing element section, which is produced, for example, from one workpiece by a turning or milling operation or as a casting by means of a suitable casting mold. A first sealing element section and a further identical second sealing element section may thus be arranged as a pair in a simple manner to form a sealing element, a factor which is very cost-effective.
A further improved sealing effect in the gap may be achieved by virtue of the fact that, in a preferred configuration, the first sealing element section and the second sealing element section overlap in the circumferential direction. A possible axial leakage flow is effectively obstructed by the overlapping in the circumferential direction. In this case, the first sealing element section and the second sealing element section may each have a slot-root sealing edge adjoining the slot root surface and a rotary edge located opposite the slot-root sealing edge in the radial direction, the rotary edge comprising the rotary region. During operation of the rotor, i.e. under the effect of centrifugal force, the slot-root sealing edge of the first sealing element section and the slot-root sealing edge of the second sealing element section in each case come into contact with the slot root surface and seal the gap. In this case, the system of sealing element sections is configured in such a way that sealing of the gap, in particular in the axial direction, is achieved by the overlapping of the sealing element sections in the circumferential direction, the sealing element sections advantageously complementing one another in their sealing effect.
The first sealing element section and the second sealing element section are preferably arranged axially adjacent to one another. In this case, the sealing element sections may also adjoin one another, a mutually mechanically stabilizing system of sealing element sections being provided for. This helps the sealing element sections to slide along one another in order to reach their precise respective sealing position during operation of the rotor. In this case, the specified system of sealing element sections is designed in such an adapted manner that it adjusts itself under the effect of the external forces, such as, for example, the centrifugal force and the normal and bearing forces, in order to achieve the desired sealing effect in the gap. Here, in the paired arrangement of the two sealing element sections to form a sealing element, especially good positive locking in the gap, in particular at the slot root surface, is realized.
The sealing element is preferably made of a high-temperature-resistant material, in particular a nickel-base or cobalt-base alloy. In addition, these alloys also have sufficient elastic deformation properties. The material of the sealing element is preferably selected so as to match the material of the rotor, as a result of which impurities or diffusion damage are largely avoided. Furthermore, a uniform thermal expansion or contraction of the rotor is ensured with the sealing element.
The fluid-flow machine is preferably a gas turbine.
An object which relates to a sealing element for a rotor of a fluid-flow machine may be achieved according to the invention by a sealing element, in particular for a rotor of a fluid-flow machine, which has a first sealing element section and a second sealing element section which are movable relative to one another, and a first rotary region having a first rotary axis is assigned to the first sealing element section, and a second rotary region having a second rotary axis is assigned to the second sealing element section, the mass center of the first sealing element section being arranged relative to the first rotary axis and the mass center of the second sealing element section being arranged relative to the second rotary axis in such a way that the torques resulting on both sealing element sections under an effect of a force are opposed. In this case, the effect of a force on both sealing element sections, for example in a rotating system, may be caused by the centrifugual force. In a fluid-flow machine, e.g. a gas or steam turbine or a compressor, including a rotor which extends along a rotation axis and has a rotor-shaft slot having a slot root surface and a moving blade having a blade root, the blade root being inserted into the rotor-shaft slot, the sealing element is especially suitable for sealing a gap formed between the blade root and the slot root surface. In this case, the gap is sealed off from possible leakage flows, for example of an action fluid or a cooling medium. However, the sealing element may also be used in other rotating systems in which a fluid flow, in particular a leakage flow, is to be sealed. Possible applications of the sealing element are, for example, in rotors or impellers of prime movers or driving machines which have hydraulic and/or pneumatic systems containing a fluid, e.g. an operating medium or lubricant (oil), and in internal combustion engines or aircraft engines containing an operating medium.
The first sealing element section and the second sealing element section preferably have similar geometry. By symmetry operations such as rotation or mirror inversion or combinations of rotation and mirror inversion, the first sealing element section and the second sealing element section may therefore be transformed into one another. An especially advantageous configuration includes the first sealing element section being and the second sealing element section being components which are identical from the design point of view. In this way, only one component needs to be produced, this component being produced, for example, as a casting by means of a casting mold or by a turning or milling operation.